Static focus ultrasound apparatus and method

ABSTRACT

An ultrasound system that utilized a transducer assembly having elements distributed in two dimensions in conjunction with a beamformer that, for each beam to be formed, samples the output of each utilized element based on a preset delay value selected for each element utilized to form the beam to form a c-scan like set of data.

BACKGROUND OF THE INVENTION

[0001] Ultrasound transducer assemblies emit ultrasound pulses andreceive echoes. In general an ultrasound assembly emits pulses through aplurality of paths and uses the received echoes from the plurality ofpaths to generate a cross-sectional or volumetric image.

[0002] Such operation is typically termed “scanning”, “sweeping”, or“steering” a beam. In most ultrasound systems, scanning is rapidlyrepeated so that many images (“frames”) are acquired within a second oftime.

[0003] Real-time sonography refers to the presentation of ultrasoundimages in a rapid sequential format as the scanning is being performed.Scanning is either performed mechanically (by physically oscillating oneor more transducer elements) or electronically. By far, the most commontype of scanning in modern ultrasound systems is electronic wherein agroup of transducer elements (termed an “array”) are arranged in a lineand excited by a set of electrical pulses, one pulse per element, timedto construct a sweeping action.

[0004] In a linear sequenced array, an aperture is swept across thearray by exciting sequential (and overlapping) sub-groups of transducerelements. In a linear phased array, all (or almost all) the elements areexcited by a single pulse, but with small (typically less than 1microsecond) time difference (“phasing”) between adjacent elements, sothat the resulting sound pulses pile up along a specific direction(termed “steering”). In addition to steering the beam, the phased arraycan focus the beam, along the depth direction, by putting curvature inthe phase delay pattern. More curvature places the focus closer to thetransducer array, while less curvature moves the focus deeper. Delay canalso be used with a linear sequenced array to provide focusing.

[0005] When an array is receiving echoes, the electric outputs of theelements can be delayed so that the array is sensitive in a particulardirection, with a listening focus at a particular depth. This receptionfocus depth may be increased continually as the transmitted pulsestravel through the tissue of the subject being imaged, focusing alongthe entire depth of the beam. This continual changing reception focus iscalled dynamic focusing. The combination of transmission focus anddynamic reception focusing greatly improves detail resolution over largedepth ranges in images.

[0006] The apparatus that creates the various delays is called abeamformer. Known beamformers have traditionally operated in the analogdomain employing expensive beamforming circuits capable of delivering anew point of data (dynamically delayed) every nano-second. Morerecently, digital beamformers, that provide delay by varying read timesout of a digital memory, have been developed. While digital beamformersrequire extensive memory, exact clock devices and large timing tables,these components are cheaper and smaller than their analog counterparts.Such digital beamformers hold out the hope of cost effective portableultrasound devices nearly as powerful as their stationary brethren.

[0007] Known portable ultrasound devices use a 1-D transducer assembly(known available devices use linear sequenced arrays) in the probe toproduce an image taken on a plane that extends from the face of theprobe. Currently, there are two classes of portable ultrasound devices:ultrasound specific devices and PC add-on devices.

[0008] Ultrasound specific devices are simply miniaturized ultrasounddevices, typically with digital beamformers, that replicate larger standalone units. One example of such a device is the SONOSITE devicemarketed by SONOSITE, INC. Unlike laptop computers, much of thecircuitry and software in large top-of-the-line ultrasound systems isnot suitable for miniaturization. Larger traditional components, such asbeamformers, lose functionality when miniaturized. PC add-on devicesattempt to integrate a transducer assembly and a beamformer in a probehousing. The probe is then connected to a PC, typically a well equippedlaptop, to perform image creation from the beamformed data. One exampleof such a device is the TERASON 2000 by TERASON.

[0009] Another area of ultrasound technology receiving significantattention are probes having a transducer assembly comprising a matrix ofelements (for example a 56×56 array of 3,136 elements), sometimesreferred to a 2-D or matrix probe. Because matrix probes allow beamsteering in 2 dimensions as well as the aforementioned focus in thedepth direction, current efforts are related to using matrix transducerassemblies for the capture of a volume of ultrasound data to be used torender 3-D images. Unfortunately, the commercialization of largereal-time full bandwidth 3-D images is probably a couple of years offdue to lack of affordable image processing resources capable of actingon the volume of data produced by matrix transducers in real-time. Todate no known available portable ultrasound devices utilize a matrictransducer assembly, probably due to the expense involved with theimplementation of a traditional dynamic focusing beamformers multipliedby the number of elements in a matrix probe that must be sampled.

[0010] Ultrasound imaging has always involved a tradeoff between imagequality and the image processing resources required to process the datafrom the transducer to obtain the results desired by the user. While therate at which data can be acquired is limited by physics (sound onlytravels so fast in the human body), the types of image processing thatcan be performed on the data is limited by the amount and quality ofimage processing resources that can be brought to bear upon the data. Ifreal time imaging is desired, as it usually is, another limiting factoris the rate of data acquisition of the processing system.

[0011] Ultrasound data is typically acquired in frames, each framerepresenting a sweep of ultrasound beams emanating from the face of atransducer. 1-D transducers produce a 2-D rectangular or pie-shapedsweep. 2-D transducers are capable of producing sweeps forming apre-defined 3-D shape, or volume. It is estimated that to fully processa relatively large volume (60°×60°) of ultrasound data in real time, abeamformer capable with 16× parallelism is required. Such a beamformerwould be prohibitively expensive, especially in a market where theacceptable cost of ultrasound systems is rapidly decreasing. Currentefforts are focused on ways to short cut full processing while bringingto market a 3-D ultrasound system capable of producing acceptable imagesat a price point competitive with current 2-D systems. No known portable3-D solutions are currently available.

[0012]FIG. 1 is a block diagram of a known 3-D ultrasound imaging system100 described in co-pending U.S. patent application Ser. No. 09/633,480assigned to the assignee of the present application. The apparatusdescribed in the 09/633,480 application uses interleaving to render a3-D image with the appearance of a real-time image from data produced bya matrix transducer assembly. This allows the use of relatively standardcomponents to minimize cost while providing a state of the art display.The system shown in FIG. 1 is, at the present time, is not available ina portable package.

[0013] The ultrasound system 100 utilizes a standard personal computer(“PC”) 102, to act as a 3-D image processor and preferably produces animage using interpolated data. The ultrasound system 100 has a matrixtransducer assembly 104 and utilizes the concept of sub-groupbeamforming. In the Example shown in FIG. 1, only elements 106 a through106 f are illustrated, but those of ordinary skill in the art willrecognize that any number of elements can be utilized. The transducer104 is preferably configured for sub-group beamforming using a series ofASICs 108 n. The use of sub-groups in beamforming is described in U.S.Pat. No. 5,997,479 and U.S. Pat. No. 6,126,602, both assigned to theassignee of the present application, the subject matter of each beingincorporated herein by reference.

[0014] Two ASICs 108 a and 108 b are illustrated, corresponding toelements 106 a-f. In the example shown each ASIC 108 n is connected tothree (3) elements although other designs are possible, for example, 5,15, or 25 elements could be connected to each ASIC 108 n. Each ASIC 108n is provided with a plurality of delay circuits 110 n (one for eachelement connected to the ASIC 108 n) that delay the output of aconnected element 106 n by a programable amount in a known manner so asto focus and steer acoustic beams. A sum circuit 112 n combines theoutput of the delay circuits 110 n in each ASIC 108 n.

[0015] The output of each ASIC 108 n is provided to a scanner 114,preferably located in a main housing of the ultrasound system 100, tocomplete beamforming. The output of each sum circuit 112 n from eachASIC 108 n is first A/D converted by a corresponding A/D converter 116n. The converted output of each sum circuit 112 n is then delayed by acorresponding delay circuit 118 n and subsequently summed with otherdelayed converted outputs by a sum circuit 120. Circuitry to performimage detection (not shown) is provided, perhaps as part of the sumcircuit 120 to produce echo data by performing an image detectingprocedure on the summed signal. A scanner control circuit 124 controlsthe timing and operation of the scanner 114 and transducer 104 usingdelay coefficients stored in a memory 122. In the case of the systemshown in FIG. 1, the delay in each of the delay circuits 110 n is keptstatic throughout reception of a single beam, but the delay in the delaycircuits 118 n are dynamically varied during reception to achievedynamic focusing.

[0016] The output of the scanner 114 is sent to a back-end 126, providedin the main housing, via an I/O 128 for subsequent signal processing.The back-end 126 performs 2-D signal processing, while the PC 102performs 3-D image processing. The back-end 126 is provided with a scanconverter 130 which converts the 2-D scan data into X-Y space.Subsequent to scan conversion, an image processing unit 131 is providedthat can be configured to perform a variety of 2-D image enhancementprocesses, such as color flow, Doppler, ect . . . , to create image datafor display on a monitor 140.

[0017] A channel link transmitter 132 transfers the echo data receivedby the back-end 126 to the PC 102 which receives the echo data via achannel link receiver 134. The channel link can be formed using chippairs, available from a variety of manufacturers, that conform to theLow Voltage Differential Signaling standard. As shown, the datatransferred to the PC 102 is obtained from a data bus in the back end126 prior to scan-conversion.

[0018] A CPU 136 performs computational tasks, including 3-D scanconversion (into X-Y-Z space) under the control of programs stored inmemory 138. The CPU 136 creates display data which forms the basis forsubsequent output to a monitor 140 (via, for example, an AGP video card(not shown)). The PC 102 performs 3-D rendering and 3-D datamanipulation, with the assistance of an expansion card, such as theVOLUMEPRO series of cards supplied by MITSUBISHI. 3-D rendering, as isknown to those of ordinary skill in the art, turns 3-D data into datasuitable for display on a 2-D screen. The first step in the renderingprocess is to identify a plane to be imaged along with a point of view.The data set is then sliced and rendered from the selected point ofview. Sometimes, the plane is volume rendered, that is enhanced withdata from parallel planes “behind” the selected plane. Overall, thedifferences between images produced by a 3-D system (termed hereinafter“3-D images”) and those produced by a conventional 2-D system are: a) a3-D image may have an arbitrary orientation with respect to the face ofthe probe; and b) a 3-D image can be volume rendered to include imagedata from nearby slices giving the illusion of depth.

[0019] The apparatus illustrated in FIG. 1 is fairly representative ofcurrent 3-D ultrasound systems in that a significant amount ofprocessing resources and complex signal processing devices are requiredto produce a rendered image. In the end though, what is often producedis still essentially a two dimensional image. One of the main concernsfor designers of 3-D ultrasound systems is how to produce an image fordisplay from the volume of data. As above, most methods revolve aroundidentifying a plane of interest and displaying data from that plane andpossibly sightly behind the plane.

[0020] The present inventors have recognized that, in effect, one of thesignificant contributions of a matrix probe is the ability to image anarbitrary plane within a volume of data. From this, they have discoveredapparatus and methods for using a matrix probe to directly image anarbitrary geometry within the field of view of the probe. This allowsthe presentation of a 2-D image substantially similar to one produced bya conventional 3-D ultrasound system without the need for a significantamount of processing resources or complex signal processing devices. Thepresent inventors have further discovered apparatus and methods forcreating a portable ultrasound device that utilizes a matrix probe.

BRIEF DESCRIPTION OF THE DRAWINGS

[0021] An understanding of the present invention can be gained from thefollowing detailed description of the invention, taken in conjunctionwith the accompanying drawings of which:

[0022]FIG. 1 is a block diagram of a known ultrasound imaging system.

[0023]FIG. 2 is a drawing illustrating a method of using an ultrasoundimaging system in accordance with preferred embodiments of the presentinvention.

[0024]FIG. 3 is a drawing illustrating a method of using an ultrasoundimaging system in accordance with the preferred embodiments of thepresent invention.

[0025]FIG. 4 is a drawing illustrating a method of using an ultrasoundimaging system in accordance with the preferred embodiments of thepresent invention.

[0026]FIG. 5 is a block diagram of an ultrasound imaging system inaccordance with a first preferred embodiment of the present invention.

[0027]FIG. 6 is a block diagram of an ultrasound imaging system inaccordance with a second preferred embodiment of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0028] Reference will now be made in detail to the present preferredembodiments of the present invention, examples of which are illustratedin the accompanying drawings, wherein like reference numerals refer tolike elements throughout.

[0029] The present inventors have discovered that, contrary toconventional wisdom, by foregoing dynamic focusing and using a matrixprobe an acceptable 2-D C-scan-like image can be produced with minimalhardware and processing resources. The present inventors have invented anew imaging method that takes advantage of a matrix transducer assemblyto produce excellent quality 2-D images that have several advantagesover 2-D images produced by convention 1-D probes. Significantly,apparatus constructed to take advantage of this method avoids the use ofcostly state-of-the-art beamformers, making it suitable for portablesystems. Such a system may also be used to present an acceptable 3-Dimage by obtaining a slab of data.

[0030] The apparatus set forth in the present application is preferablyspecifically constructed for the required purpose, i.e. ultrasoundimaging, but the methods recited herein may operate on a general purposecomputer or other network device selectively activated or reconfiguredby a routine stored in the computer and interface with the describedultrasound imaging equipment. The procedures presented herein are notinherently related to any particular ultrasonic system, computer orother apparatus. In particular, various machines may be used withroutines in accordance with the teachings herein, or it may prove moreconvenient to construct more specialized apparatus to perform therequired method steps. In certain circumstances, when it is desirablethat a piece of hardware possess certain characteristics, thesecharacteristics are described more fully in the following text. Therequired structures for a variety of such hardware may appear in thedescription given below. Machines which may perform the functions of thepresent invention include those manufactured by such companies asAGILENT TECHNOLOGIES, and ADVANCED TECHNOLOGY LABORATORIES, INC., aswell as other manufacturers of ultrasound equipment.

[0031] With respect to the methods described herein, those of ordinaryskill in the art will recognize that there exists a variety of platformsand languages for creating software for performing such methods. Thoseof ordinary skill in the art also recognize that the choice of the exactplatform and language is often dictated by the specifics of the actualsystem constructed, such that what may work for one type of system maynot be efficient on another system.

[0032]FIG. 2 is a drawing illustrating a method of using an ultrasoundimaging system in accordance with preferred embodiments of the presentinvention. FIG. 2 shows a 6×6 matrix transducer assembly 204 withrepresentative beams (also referred to as “scan lines”) formed inaccordance with the present invention. Each scan line is formed by a setof individual acoustic path lines from each element 206 n (only elements206 a through 206 f are labeled for ease of explanation) terminating ata particular focus points 242 a through 242 i.

[0033] Those of ordinary skill in the art will realize that FIG. 2 isjust a conceptual representation of the operation of the transducerassembly 204 in that the signal from and to each element does notperfectly travel along the lines shown therein, rather the lines andfocal points are representations of the effect of the signals output byeach elements 206 n based on the delays imparted to the drive signal foreach element 206 n. In general, each focal point 242 n represents thedata obtained from a single scan line, or “beam,” while the collectionof focal points 242 a-242 i represents a single frame.

[0034] Only focal points 242 a-242 i are portrayed so as to keep theillustration understandable. However, those of ordinary skill in the artwill recognize that the number of scan lines per frame is a designchoice based on a trade-off between resolution and frame rate.

[0035] Preferably, more lines per frame are generated than in acorresponding 1-D probe equipped system. In general, the number of scanlines per frame should be selected using the same criteria for suchselection in a conventional 3-D imaging system.

[0036] In accordance with a preferred embodiment of the presentinvention, the receive delays for each scan line, in the set of scanlines (for example, a frame), are set to be equal to the time of flightto and from the focal point along the respective lines from eachelement. The delays for each of the elements 206 n scan line are said tobe static. In other words, while the receive delays for each element mayvary as between different beams, for any given beam they are constantfor the entire receive process of that beam. While preferable, thereceive delay for each element does not necessarily have to coincidewith the time of flight to and from the transmit focus, as describedherein below.

[0037] Each of the focal points 242 n lie on a predetermined arbitrarygeometric shape, for example a planar surface, a curved surface, orother shapes such as frusto-conical (referred to as an “arbitrarygeometry”). In a sense, the continuous receive focus achieved by 1-Dprobes over a plane extending from the probe face is replaced throughthe use of a matrix probe and static focus. Instead of focusing atmultiple receive points on a plane extending from the probe, the presentinvention focuses at a single point per scan line wherein the focuspoints lie on an arbitrary geometry, in effect giving dynamic focus overthe surface of the imaged shape. Preferably the focus points areco-planner, although those of ordinary skill in the art will recognizethat other shapes, such as concave or convex curves, may be usefuldepending on the subject being imaged.

[0038] The scan lines may occupy a pyramidal or frustum shape, or may beparallel (for a “linear” format). If a parallel shape is utilized, thescan view will be the same size as the probe aperture. If a frustumshape is used the scan view may be lager than the probe aperture,however, depending on the focus depth, more scan lines may be needed toachieve a similar resolution to that obtained with the parallel shape.

[0039] When used to image an arbitrary plane, the scan produced inaccordance with the present invention is similar to a type of scancalled a “c-scan.” In general, the term “c-scan” refers to a scan of anyplane that does not intersect the transducer. The present inventionproduces a scan similar to a c-scan, in that it does not necessarilyintersect the transducer (although with proper selection of delays theimaging plane may intersect the probe face). As noted, the presentinvention is not limited to a plane, but can image any arbitrarygeometry. Further, in accordance with the present invention, anddiffering from the traditional notion of a c-scan, the c-scan producedby the present invention may have thickness. The data produced by a scanin accordance with the present invention can represent as much thicknessas can be imaged by the overlap of transmit and receive beams. Thus, thedata set produced by the present invention may represent a “slab” havinga thickness roughly equal to or less than the depth of field of the scanlines. The static transmit and receive foci may be displaced from oneanother by a short distance to increase the composite beam's effectivedepth of field, thereby increasing the depth of the slab.

[0040] In displaying the resulting slab of data at least two techniquescan be employed. First, it can be treated as a matrix of data, slicedand rendered as with a full volume matrix. In other words, the slab canbe rendered into a 3-D image using known methods, including the 2-Ddisplay of a slice of the slab. Controls can be provided on theultrasound system to allow the user to adjust the thickness of the slaband/or the depth of the slice imaged. Second, the data in the slab canbe accumulated (or averaged) over the depth of each beam.

[0041] In summary, in exchange for preselecting the plane to be viewed,acceptable 3-D images can be produced with a limited data set which, asdescribed herein below, may be obtained with a highly simplifiedbeamformer. One way to think of the present invention is that instead ofobtaining data from an entire volume and slicing to get a view, thepresent invention gets data directly from the sliced surface.

[0042] The shape and orientation of the imaged plane, shape or slab maybe selected based on the structure being imaged. For shallow peripheralvascular scanning a scan plane parallel to the skin may be selected witha shallow focal point. As the depth of the slab is more or lessconstant, the user may simply sweep over the patient for a view of thesubcutaneous layer. Using known techniques, such as image correlation, asequence of images can be spliced together to provide the user with alarge map. As another example, by tilting the slab past 45 degrees,standard cardiac views can be replicated in a transthoracic probe. FIGS.3 and 4 show further examples of useful scan plan orientations.

[0043]FIG. 3 is a drawing illustrating a method of using an ultrasoundimaging system in accordance with the preferred embodiments of thepresent invention. FIG. 3 shows a 6×6 matrix transducer assembly 304with representative scan lines formed in accordance with the presentinvention. In particular, FIG. 3 shows scan lines emanating from avirtual scan origin above the face of the transducer assembly 304 andfocusing on focus point 342 n. The acoustic paths to each element havebeen eliminated for clarity. In this case a scan plane 344 has beenformed roughly parallel to the face of the transducer assembly 304. Thisconfiguration facilitates the imaging of structures near the surface ofthe skin by providing a field of view significantly larger than thephysical aperture. As is known to those of ordinary skill in the graphicart, data from multiple frames can be concatenated to form an imagehaving an area greater than the area of an image in any one frame.

[0044] Scan lines can also be formed so as to create a virtual apexbelow the face of the transducer assembly 304. This has been referred toa “keyhole” scanning ans is particularly useful for scanning thoughsolid structures, such as ribs, or around other impediments.

[0045]FIG. 4 is a drawing illustrating a method of using an ultrasoundimaging system in accordance with the preferred embodiments of thepresent invention. FIG. 4 shows a 6×6 matrix transducer assembly 404with representative scan lines formed in accordance with the presentinvention. In particular, FIG. 4 shows scan lines emanating from avirtual scan origin at the face of the transducer assembly 404 andfocusing on focus point 442 n. A scan plane 544 is formed skewed fromthe face of the transducer assembly 404. By adjusting the skew of theplane, views comparable to views produced by 1-D transducers can bereplicated and even improved. For example, it is possible to produce a“true” short axis view of the left ventricle valves showing an accuratecross-section thereof.

[0046] The present invention, as described with respect to FIGS. 2-4 canbe implemented on a variety of ultrasound systems. FIGS. 5 and 6 areexamples of two architectures optimized for the present invention.However, those of ordinary skill in the art will recognize that thepresent invention can be practiced on current architectures utilizingtraditional dynamic delay beamformers even though the most expensivehardware in such systems would be severely under-utilized.

[0047]FIG. 5 is a simplified block diagram of an ultrasound imagingsystem 500 in accordance with the preferred embodiment of the presentinvention. The ultrasound system 500 is based on existing technologyoptimized for the present invention. It will be appreciated by those ofordinary skill in the relevant arts that the ultrasound imaging system500, as illustrated in FIG. 5, and the operation thereof as describedhereinafter is intended to be generally representative such systems andthat any particular system may differ from that shown in FIG. 5,particularly in the details of construction and operation of suchsystem. FIG. 5 is a simplified diagram that illustrates the inventivefeatures of the present invention. Those of ordinary skill in the artwill recognize that certain components have been omitted so as toenhance understanding of the present invention, including for examplereceive filters. As such, the ultrasound imaging system 500 is to beregarded as illustrative and exemplary and not limiting as regards theinvention described herein or the claims attached hereto.

[0048] The ultrasound system 500 utilizes a processing unit 502,preferably, but not necessarily, embodied by a standard personalcomputer (“PC 502”), to act as an image visualization unit. Theultrasound system 500 is provided with a matrix transducer assembly 504.In the Example shown in FIG. 5, only elements 506 a through 506 f areillustrated, but those of ordinary skill in the art will recognize thatany number of elements can be utilized, for example a 48×60 elementarray is but one option.

[0049] The transducer assembly 504 is preferably configured forsub-group beamforming using a series of ASICs 508 n. The ASICs 508 n arepreferably based on the ASICs 108 n. Two ASICs 508 a and 508 b areillustrated, corresponding to elements 506 a-f. In the example shown,each ASIC 508 n is connected to three (3) elements. Depending on thelevel of integration, any number of elements, for example 25, 75, 120,150, etc . . . could be connected to each ASIC 508 n. However, inaccordance with the preferred embodiment 20 elements are grouped by eachASIC 508 n. Each ASIC 508 n is provided with a plurality of delaycircuits 510 n (one for each element connected to the ASIC 508 n) thatdelay the output of a connected element 506 n so as to focus and steeracoustic beams.

[0050] In accordance with the prior art, the reception delay is staticfor any given delay circuit 510 n with respect to any given beam.Therefore, the delay elements 510 n do not need to be capable of dynamicreception focusing. This allows the use of relatively cheap and smallcircuits for the delay circuits 510 n. While such beamforming circuitsare known, current conventional wisdom calls for the use of dynamicdelay beamforming circuits capable of dynamic reception focusing inalmost every application. The present invention dispenses with suchcomplicated circuitry while achieving the benefits provided thereby. Itis to be noted, that ultrasound apparatus utilizing convention dynamicdelay beamformers can be used in accordance with the methods of thepresent invention, for example by disabling the dynamic receptionfocusing. It is noted that dynamic reception focusing need not be“disabled” rather, the system would only sample data from the arbitrarygeometry.

[0051] While the lack of dynamic reception focusing severely limits thedepth of field obtainable with the probe 104, acceptable 2-D images maybe obtained using this configuration, and, as discussed herein above,provide some significant advantageous over 2-D images obtained withconventional 1-D probes. The configuration shown in FIG. 5 isparticularly suitable for portable ultrasound devices in that it uses aminimal amount of space and a minimal amount of power.

[0052] A sum circuit 512 n combines the output of the delay circuits 510n in each ASIC 508 n. A sum circuit 514 combines the output of each ofthe sum circuits 512 n in each of the ASICs 508 n. Preferably, 2880elements 506 n are grouped into 144 sub-groups of twenty (20) elementseach. Preferably, 128 of the 144 sub-groups are used for imaging,requiring 128 ASICs 508 n, the output of which are summed by the sumcircuit 514.

[0053] The output of the sum circuit 514 is A/D converted by an A/Dconverter 516 and sent to the PC 502 via a communication link comprisingI/O controllers 518 and 520 along with transmission medium 519. Inaccordance with the preferred embodiment, the communication link is aUniversal Serial Bus (“USB”) link. USB is an industry standard interfacefor connecting peripherals to a PC and provides up to 2.5W at 5V to theconnected peripheral.

[0054] The USB 1.1 standard currently in use allows data rate up to 12Mbits/sec. Utilizing the USB isochronous transfer protocol, periodicbursts of data at 60 Mbits/sec are possible. Such a rate is sufficientfor RF capture from an ultrasound probe. In the future USB standard 2.0will provide a transfer rate of 480 Mbits/sec. Those of ordinary skillin the art will recognize the applicability of other interfaces such asIEEE 1394 (known as “FIREWIRE”). Additionally, depending on theimplementation of the present invention, direct connections to a PCI busor parallel port are feasible. The connection to the PCI bus can be viaa PCI card or even a PC card. If data is compressed prior to transfer,other options exist, such as lower speed serial connections.

[0055] Each of the I/O controllers 518 and 520, can comprise, forexample a low-power USB ICs available from CYPRESS SEMICONDUCTOR. SuchICs typically contain enough RAM to store one line of beamformed dataand an 8051 based micro-controller for coordinating the isochronoustransfer to the PC. An interesting benefit for this design is that theclock for the ASICs 508 n and the line timing can come from the USBtransfer itself: while one transfer is occurring, the clock is providingfor the next line's acquisition and storage in RAM.

[0056] The output of the sum circuit 514 is converted to an amplitude“envelope” signal (referred to a “echo data”) representing tissuebrightness vs. time by an image detector 521. The envelope signal issubsequently stored in a memory 524 within the PC 502 under thedirection of a CPU 522. A scan conversion process 526 acts on thedigital data to produce data for eventual display by a display adapter528 on a monitor 530. The CPU 522 controls the timing and operation ofthe transducer 504 using delay coefficients calculated and/or stored inthe memory 524.

[0057]FIG. 6 is a block diagram of an ultrasound imaging system 600 inaccordance with a second preferred embodiment of the present invention.The device shown in FIG. 6 represents a departure from traditionalbeamformer design and is highly optimized for use with the presentinvention eschewing all unnecessary hardware. It will be appreciated bythose of ordinary skill in the relevant arts that the ultrasound imagingsystem 600, as illustrated in FIG. 6, and the operation thereof asdescribed hereinafter is intended to be generally representative suchsystems and that any particular system may differ from that shown inFIG. 6, particularly in the details of construction and operation ofsuch system. FIG. 6 is a simplified diagram that illustrates theinventive features of the present invention. Those of ordinary skill inthe art will recognize that certain components have been omitted so asto enhance understanding of the present invention, including for examplereceive filters and detectors. As such, the ultrasound imaging system600 is to be regarded as illustrative and exemplary and not limiting asregards the invention described herein or the claims attached hereto.

[0058] The ultrasound system 600 utilizes a processing unit 602,preferably, but not necessarily, embodied by a standard personalcomputer (“PC 602”), to act as an image visualization unit. Theultrasound system 600 is provided with a matrix transducer assembly 604having a matrix of elements 606 n. As with the Example shown in FIG. 5,only a couple of elements are illustrated, but those of ordinary skillin the art will recognize that any number of elements can be utilized(for example a 48×60 element array).

[0059] The ultrasound system 600 uses quadrature to facilitate thedetection of echo data. This alleviates the need for a dedicated imagedetector. Each element 606 n is connected to two switches 608 n 1 and608 n 2. If the use of quadrature is not required only a single switchper element would be necessary. The operation of the switches iscontrolled by a controller to be discussed hereinafter. Basically, eachswitch acts as a sampler by closing at a specified time to permit asignal from an associated element describing a single locus on anarbitrary geometry to be collected. This locus can be thought of as afocus point, although perfect focus is not necessary. The switches 608can be constructed to hold a remotely supplied time value or can beactivated by a control signal. Each pair of switches 608 n 1 and 608 n 2are closed in sequence, with the switch 608 n 2 being timed to close ata time after 608 n 1 equivalent to ¼λ where λ is the period of thefundamental frequency of the ultrasound waveform. Specifically, each ofthe first switches 608 n 1 are programed or controlled to close based onthe static focus value for the associated element and each of the secondswitches 608 n 2 are programed to close ¼λ after its associated firstswitch.

[0060] To obtain a slab of data the switches 608 can beconfigured/controlled so as to open and close a predetermined number oftime so as to obtain a burst of samples. In fact, such “burst operation”can be used to obtain samples from the entire depth of the beam.

[0061] The outputs of the first switches 608 n 1 are summed by a I sumcircuit 610 a, while the outputs of the second switches 608 n 2 aresummed by an Q sum circuit 610 b. The outputs of the I sum circuit 610 aand the Q sum circuit 610 b are converted to digital data via an A/Dconverter 622 (ADC 622) and transmitted to the processing unit 602 via acommunication link comprising I/O controllers 612 and 614 along withtransmission medium 613. The communication link may, for example,comprise a Universal Serial Bus (“USB”) link or an IEEE 1394 link.However, in accordance with the second preferred embodiment, thecommunication link is implement using a direct connections to a main bus626 of the processing unit, and more preferably, is implemented usingthe PC card standard.

[0062] The PC Card standard is set by the Personal Computer Memory CardInternational Association (PCMCIA) and currently has threeimplementations designated Type I, Type II, and Type III. Each of thetypes provides for a 16 bit bus, with each type being progressivelythicker (allowing for more circuitry). Additionally, the PCMCIA hasissued an extension of the PC Card Standard, referred to as CardBus,that provides a high speed 32-bit bus. The present invention can equallybe implemented using a CardBus. Details on implementing thecommunication like using either the PC Card standard or the CardBusstandard are not germane to the present invention, but is suffices tosay that those of ordinary skill in the art will be able to effectivelyimplement either solution based on the teachings contained herein.

[0063] Once the signals from the I sum circuit 610 a and the Q sumcircuit 610 b are received by the I/O controller 614, they are squaredby squaring circuits 616 a and 616 b and subsequently summed into asingle signal by an adder 618. The output of the adder 618 is integratedby integrator 620.

[0064] The I/O controller 614, squaring circuits 616 a and 616 b, adder618, and integrator 620 are preferably incorporated into a PC Card 636for interface with the main bus 626 of the PC 602. Further a controlcircuit 624 is provided on the PC Card 636 to control operation of thevarious components and to act as an interface with the switches 608.Alternatively, a switch control signal can be provided by the PC 602.

[0065] The output of the integrator 620 is provided to a main bus of thePC 602 for subsequent display. The PC 602 is provided with a memory 628,CPU 630 and display adapter 632 as is known in the art. Once the CPU 630has transformed the data from the matrix transducer assembly 604 intodisplayable data, a process well known to those of ordinary skill in theart, an image is displayed on the monitor 634 by the display adapter632.

[0066] It will be recognized that an analog communication link can beanalog and the squaring circuits 616a and 616b, adder 618, integrator620 be formed in analog circuitry. An ADC would then be provided todigitize the output of the integrator 620 prior to loading the resultantdata into the memory 628.

[0067] Although several examples of the present invention have beenshown and described, it will be appreciated by those skilled in the artthat changes may be made in the described examples without departingfrom the principles and spirit of the invention, the scope of which isdefined in the claims and their equivalents. For example, the ultrasoundsystem 600 can be modified to provide limited dynamic focusing byupdating the delay values feed to the switches 608 n. Additionally, mostconventional imaging modes, such as Doppler and harmonic, can be used inconjunction with the apparatus and methods of the present invention.Further, it is possible to simulate a matrix probe using a mechanicalwobbler and either a single element array or a linear array.

What is claimed is:
 1. An ultrasound system comprising: a transducerassembly having a plurality of elements distributed in two dimensions;and a beamformer that, for each beam to be formed for each frame,samples the output of each utilized element so as to generate datawithin a slab centered about a selected point for each beam, thethickness of the slab being substantially less than the usable depth ofthe transducer.
 2. The ultrasound system, as set forth in claim 1,wherein the beamformer samples the output of each utilized element so asto generate data for the selected point for each beam.
 3. The ultrasoundsystem, as set forth in claim 1, wherein the beamformer generates datafor a plurality of points, one point for each beam, on an arbitrarygeometry in each frame.
 4. The ultrasound system, as set forth in claim1, further comprising: a processor that receives data from thebeamformer and produces data suitable for display.
 5. The ultrasoundsystem, as set forth in claim 4, further comprising: a first housingintegrating the transducer and the beamformer; and a second housingsupporting the processor.
 6. The ultrasound system, as set forth inclaim 4, wherein the processor is configured to provide delay values tothe beamformer.
 7. The ultrasound system, as set forth in claim 4,wherein the processor is configured to perform a scan conversion processon the data from the beamformer.
 8. The ultrasound system, as set forthin claim 4, wherein the processor is part of a personal computer.
 9. Theultrasound system, as set forth in claim 4, further comprising: a serialinterface connecting the beamformer with the processor.
 10. Theultrasound system, as set forth in claim 9, wherein the serial interfaceis a USB interface.
 11. The ultrasound system, as set forth in claim 10,wherein the USB interface conforms with the USB 1.0, 1.1, or 2.0specifications.
 12. The ultrasound system, as set forth in claim 10,wherein the transducer assembly and beamformer are powered via the USBinterface.
 13. The ultrasound system, as set forth in claim 10, whereinthe transducer assembly and beamformer utilize a clock signal providedby the USB interface.
 14. The ultrasound system, as set forth in claim9, wherein the serial interface is an IEEE 1394 based interface.
 15. Anultrasound system comprising: a transducer assembly having a matrix ofelements; a beam former that forms a beam using a static delay for eachelement for each focal point in a frame; and a processor that receivesdata from the beamformer and produces data suitable for display.
 16. Theultrasound system, as set forth in claim 15, wherein the beam former hasa plurality of groups and an overall sum circuit that sums the output ofeach of the groups, each group comprising a plurality of elements, adelay circuit that delays the output of each element based on a valuederived from information from the processor, and a sum circuit that sumsthe output of each delay circuit in the group.
 17. The ultrasoundsystem, as set forth in claim 15, further comprising: a first housingintegrating the transducer and the beamformer; and a second housingsupporting the processor.
 18. An ultrasound system comprising: atransducer assembly having a matrix of elements; and beamformer meansthat uses a static delay during receive to produce echo data describinga slab.
 19. A method of obtaining ultrasound data comprising: isonifyinga region using a plurality of elements distributed in at least twodimensions; receiving echoes using a static focus; and displaying animage based on the received echoes.
 20. A method, as set forth in claim19, further comprising: forming a slab of data based on the receivedechoes; and wherein the step of displaying includes displaying arepresentation of a portion of the slab of data.
 21. A method, as setforth in claim 19, wherein the step of receiving includes: beamformingsignals from the matrix of elements by summing the signals with fixeddelays for each element.
 22. A method, as set forth in claim 19, furthercomprising: transmitting data from a transducer used to isonify theregion and receive the echoes to a processing unit via a serialinterface.
 23. An ultrasound system comprising: a plurality of elementsin a multi dimensional distribution that output a signal representativeof a received echo; a plurality of samplers, at least one sampler beingassociated with each element, each of the samplers being timed toacquire, for each of a plurality of acoustic events, a signal from anassociated element describing a single locus on an arbitrary geometry.24. An ultrasound system, as set forth in claim 23, wherein each elementis connected to at least two samplers.
 25. An ultrasound system, as setforth in claim 23, wherein each sampler comprises a switch thatresponsive to a control signal closes for a predetermined time after apredetermined delay.
 26. An ultrasound system, as set forth in claim 23,wherein each sampler comprises a switch that responsive to a controlsignal sequentially opens and closes a predetermined number of times fora predetermined time after a predetermined delay.
 27. An ultrasoundsystem, as set forth in claim 23, further comprising: a processor thatreceives data from the plurality of samplers and produces data suitablefor display.
 28. An ultrasound system, as set forth in claim 27, furthercomprising: an adapter card connected to the samplers and the processorthat received data from the samplers, processes said data to producedigital data representing the received echos and supplies the digitaldata to a memory associated with the processor.
 29. An ultrasoundsystem, as set froth in claim 27, wherein the adapter card is a PC card.30. An ultrasound system, as set forth in claim 27, wherein the samplerssample data from an arbitrary geometry using a virtual apex on anopposite side of the plurality of elements as the arbitrary geometry.31. An ultrasound system, as set forth in claim 27, wherein the samplerssample data from an arbitrary geometry using a virtual apex on a sameside of the plurality of elements as the arbitrary geometry.
 32. Anultrasound system, as set forth in claim 27, further comprising: animage processing unit that concatenates data from multiple frames tocreate a super-set of data describing an area greater than the areadescribed by any one frame.